1. Field of the Invention
This invention relates to a bookbinding cloth provided with a resilient adhesive layer through which a plurality of paper sheets are bound together at aligned one edges thereof.
2. Description of the Prior Art
A typical bookbinding system has been disclosed in U.S. Pat. No. 3,973,787 issued to Staats et al. A foldable book cover or bookbinding cloth is provided, at a backbone thereof, with a normally non-adhesive but thermally activatable adhesive layer. A plurality of paper sheets or the like sheet material are placed, in a gathered, edge-aligned condition, on the adhesive layer which has not yet become adhesive. Heat is then applied to the adhesive so that the aligned edge portions of the paper sheets may be secured to the backbone of the bookbinding cloth through the hot-melted, activated adhesive, which is then cooled to for solidification.
An example of the bookbinding cloth prepared in accordance with the above-described prior art bookbinding technique is diagrammatically illustrated in FIG. 9. The bookbinding cloth 1 in this example includes a backbone 2 of a predetermined width (Wb) and a pair of side extensions 3a and 3b formed integral with the backbone 2. To the backbone 2 is secured a resilient hot-melt layer 4 of thermally activatable adhesive resin material, which extends over the entire width Wb of the backbone 2 and provides a flat surface for bonding together aligned edges of a plurality of paper sheets 5 of a predetermined thickness (Wp) which should correspond to the width (Wb) of the adhesive layer 4, by applying heat to the backbone 2 to melt the adhesive material in the layer 4 followed by cooling. The side extensions 3a and 3b have a size substantially identical to or somewhat larger than the paper sheets 5 to thereby serve as front and back covers of a booklet to be produced. The adhesive layer 4 will have a sufficient thickness for assuring permanent bonding and a considerable degree of hardness in a solidified condition, which means that the adhesive layer 4 could not easily be folded in the middle of the predetermined width thereof. To meet various requirements for manufacturing booklets of different thickness (Wp), it will therefore be necessary to prepare a number of book covers which have similar construction but provide different widths (Wb) of backbones and adhesive layer attached thereto.
Another prior art bookbinding cloth has been proposed, in which a single adhesive layer in the above-described prior art is replaced by a plurality of lengthwise extending adhesive layers 4', 4' . . . 4' which are spaced apart and secured in a parallel fashion to the backbone of the bookbinding cloth 1, as can be seen in FIG. 10. Between two adjacent adhesive layers there is provided a lengthwise extending groove which may act as a crease or fold allowing the backbone to be easily folded therealong. It is understood that this prior art bookbinding technique has an advantage that a single kind of bookbinding cloth may be employed for producing booklets of different thickness, by folding the backbone along a selective one of the grooves formed between the ridge-like adhesive layers. However, when the paper sheets are placed above the backbone of this bookbinding cloth, some of them would enter the groove and others would rest on the ridge of the adhesive layer, which inevitably impairs the edge-alignment of the paper sheets in the booklet thus produced.
Japanese Utility-Model Publication No. (Sho) 56-15021 discloses a bookbinding element comprising a sheet made of thermally activatable adhesive material. The adhesive sheet has a plurality of spaced rows of slits or concaved grooves extending in a lengthwise direction. The slit row is discontinued by unslitted parts but the adhesive sheet may be splitted along a desired one of the slit rows to conform the width of the bookbinding element to a given thickness of a booklet to be produced by bookbinding. The adhesive sheet, which has been split to have a desired width, may be attached to a backbone of a book cover through a permanent adhesive layer formed on a backside of the adhesive sheet. The permanent adhesive layer is normally covered with a resin-impregnated paper, which should be peeled off just before bonding of the adhesive sheet to the backbone. This element can be widely used for bookbinding of variable thick booklets. This bookbinding element has a three-layer construction comprising the thermally activatable adhesive sheet, the permanent adhesive layer and the peel-off paper, so that the sheet splitting operation should be made with scissors, cutters or other cutting instruments.